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Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
523 FOUS30 KWBC 060034 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 834 PM EDT Fri Jul 5 2024 Day 1 Valid 01Z Sat Jul 06 2024 - 12Z Sat Jul 06 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE DEEP SOUTH... 01Z Update: ...Northeast... Convection continues to develop ahead of an approaching shortwave trough over the Northeast, with a couple focus areas of more organized convection, one near NYC metro through southern New England while another area is developing across southern NY near BGM. The expectation for the remainder of the period is that a few lines/clusters of storms will move through, relatively quickly, but there is still some potential for training/repeating rounds that could drop a quick 1-2" and cause isolated flash flooding, so the Marginal Risk and the WPC MPD remain in effect. ...Deep South... In the very warm and very moist airmass, deep convection developed across portions of Louisiana and Mississippi early this afternoon. Effective boundaries and outflows along with a favorable upper level pattern will continue the threat for slow moving, intense thunderstorms across portions of Louisiana through late this evening. 18Z HREF continues to highlight potential for isolated 2-3" hourly totals with convection near New Orleans as well as with activity in northern Louisiana that should move slowly southward into the evening hours. Some potential for a quick 2-4" of rain based on the latest HREF probabilities and the Slight Risk was adjusted to the trends. Further east into Alabama and Georgia, more isolated evening convection is expected but given the very moist airmass and environmental ingredients, isolated flash flooding will remain possible. ...New Mexico... Convection firing off the terrain in eastern New Mexico will continue to pose a heavy rainfall and flash flood risk into the late evening hours. While coverage will remain on the isolated side, intense rain rates over sensitive areas justify continuing the Marginal Risk. Taylor Day 2 Valid 12Z Sat Jul 06 2024 - 12Z Sun Jul 07 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE CAROLINAS AND THE HAMPTON ROADS OF VIRGINIA... ...20Z Update... The previously inherited SLGT risk across the Carolinas into Southeast VA was maintained with little to no changes as guidances maintains relative continuity on both coverage and magnitude of expected convection. 12z HREF probability fields indicate localized amounts exceeding 3" possible on Saturday afternoon into the evening before the loss of diurnal heating puts an end to the primary convective threat. There was reasonable coverage of 1-2" totals scattered across the I-95 corridor between Raleigh down to Columbia, SC within the blended mean forecast off the HREF with significant overlap of the highest QPF signatures from the previous ensemble bias corrected QPF footprint. Pending cell mergers and established outflows, higher totals could fall outside the SLGT in the MRGL risk area, especially across SC. There was little reason to deviate from the previous forecast given the above conditions and signals. Elsewhere, the biggest changes occurred over the Plains where the MRGL risk was expanded in all directions with the biggest additions over the Northern Plains and through parts of the TX/OK Panhandles. This was more in line with the First Guess Fields and the convective QPF footprint within the latest hi-res ensemble. There`s a greater signal further north across the Dakotas due to the favorable upper forcing pattern transpiring thanks to a shortwave trough pushing into the region. A stronger thermodynamic profile exists further south into the Southern Plains, but the signal is more isolated, but still within an environment favorable for locally heavy rainfall with rates of 1-2"/hr possible. MRGL risk across New England was maintained with some lean towards a SLGT risk addition, but wanted to give one more cycle of guidance to assess the setup and add a targeted SLGT after the convective evolution later this evening. Some of tomorrows impacts are contingent on the convective pattern at the end of D1, but there is some First Guess field support for the SLGT potential, albeit a little large in coverage than what could possibly be issued. Kleebauer ...Previous Discussion... A slow moving frontal boundary will be a focus for areas of heavy rainfall across the Gulf Coast region and much of the East Coast. A Slight risk was maintained with this update across portions of the Carolinas into southeast VA. An impressive overlap of instability and moisture is noted across this region...with CAPE likely over 2000 j/kg and PWs around 2.25" (approaching climatological 95th percentile values). Some signs that there could be at least some upper level moisture connection to Hurricane Beryl by this time as well, potentially adding to rainfall efficiency. Weaker mid/upper forcing and limited deep layer shear suggests convection will generally be disorganized and of a pulse variety. However we should see enough coverage to result in some cell mergers and clusters, which will locally enhance rainfall duration. Thus anticipate we will see pretty good coverage of heavier rainfall totals within the Slight risk area, with scattered amounts exceeding 3" likely. Dry soil conditions will be a limiting factor for flooding...however rainfall rates should be able to overcome this enough to make this a solid Slight risk. Convective coverage along the central Gulf Coast does not look as great at the moment. The latest guidance taken verbatim probably does not support a Marginal risk here, however PWs will remain elevated, a boundary will be in the vicinity, and areas of heavy rainfall are likely on day 1 potentially making things more susceptible by day 2...thus will maintain the Marginal risk. The stalled front over TX will continue to pose some heavy rainfall threat, although not expecting coverage to be all that great. Enough instability and moisture over eastern NM to suggest another round of terrain influenced diurnal convection is likely. The Marginal risk was expanded north into New England with this update. Guidance is in better agreement today that the front will still be to the west of the area, with plentiful destabilization during the day Saturday. An approaching mid level shortwave and stronger deep layer shear suggests a more organized convective potential. PWs could potentially be approaching early July max values, so the ingredients are certainly in place for heavy rainfall. We may very well eventually need a Slight risk over portions of the region...but still some questions with convective evolution, and some chance storms stay fairly quick moving off to the east. Thus did not want to go right to a Slight risk...preferring to introduce the Marginal and continue to monitor trends. A Marginal risk also extends from portions of KS into IA. Broad troughing remains over the central U.S, and guidance indicates a mid level shortwave should be diving south within the long wave trough. There is also a response in the upper jet, and overall large scale synoptic support for ascent looks pretty good by Saturday night. Not surprising that we also see a low level response to this increased forcing, with 850mb moisture transport seeing a notable uptick. Moisture looks to be a limiting factor, as still not seeing a great deep layer moisture connection, and so PWs are only forecast around or slightly above average levels. Despite only modest moisture...the strong forcing should make up for this and allow for some potentially heavy rainfall totals. Chenard Day 3 Valid 12Z Sun Jul 07 2024 - 12Z Mon Jul 08 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF KANSAS, OKLAHOMA, AS WELL AS THE CENTRAL AND SOUTHERN COAST OF TEXAS... ...20Z Update... The previous SLGT risk across South TX was expanded up the coast in the latest update. For more on this change, please refer to the, "Coastal Texas" sub-heading below... Elsewhere, the signal for significant rainfall has grown across portions of the Central and Southern Plains with the primary axis of focus lying between southern KS through the western half of OK, excluding the Panhandle. Ensemble QPF between 2-4" is now the base forecast across the outlined region with a strong mid-level disturbance and surface convergence pattern the main reason for such a prolific signal. Latest IVT forecasts continue to show somewhat of a connection with the moisture associated from Beryl streaming out ahead of the cyclone with some prolific theta-E advection towards the end of the forecast moving into the primary region of convergence. If this were to verify, an upgrade could be plausible for parts of the Southern Plains with the best chance residing over western OK down into the Red River Valley. There were no changes across the Southeast where scattered convection with isolated stronger cores could allow for locally heavy rainfall with flash flood threat confined to more urbanized settings within the confines of the Carolinas down towards the FL Panhandle. ...Coastal Texas... Biggest shift in the forecast comes across the Central and South TX coastal plain where recent trends in the track of Beryl have allowed for an expansion of the previous SLGT risk further up the TX coast while encompassing the risk area closer to the coast as the storm motion and compact storm structure is forecast to keep the heaviest precip focused along the coast. There has been a significant shift in some of the recent deterministic that now aligns well with the storms track based off recent ML output, and favors the right side of the 12z Hurricane Model tracks. The core of the cyclone is now forecast to remain over water through the D3 forecast period with the outer bands Beryl likely protruding inland as far as the immediate coast with highest certainty and further inland more likely after the current D3. Totals based on recent ensemble means have increased as a result further up into the middle TX coast with the heaviest now situated between Corpus up to Freeport. There is still some uncertainty in the northern extent of the track as some guidance continues to fall even further north of the current forecast, so this forecast is subject to shifts in the exact location of the SLGT risk, but likely still confined to the coastal plain. Kleebauer ...Previous Discussion... ...Southern and Central Plains... Organized convection is likely over portions of KS and OK Sunday into Sunday night. Quite the impressive model QPF signal...with both good run to run continuity and model to model agreement. Thus forecast confidence is above average with this event. Interestingly the pattern appears to favor a rather progressive convective complex...and PWs are not forecast to be overly high either. Thus the impressive QPF from the models, while somewhat surprising, is likely indicative of the very strong mid/upper level forcing and low level frontal convergence in play. A look at layer IVT suggests we may start to see some low level connection to the moisture plume ahead of Beryl, so this is certainly something to keep an eye on and could act to enhance rainfall efficiency. Either way this is a solid Slight risk, with the apparent progressiveness of convection keeping the risk from going higher...but will need to continue to monitor. ...Southeast... Convection along the stalled front will again pose at least an isolated flash flood threat over portions of the Southeast Sunday. PWs will remain above the climatological 90th percentile, and layered IVT suggest we may see some mid/upper level moisture connection to Beryl. This could help increase rainfall efficiency in what will already be a favorable environment for heavy rainfall rates. Chenard Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt